THU0147 Comparison of biological hasards of 166-holmium-phytate and 90-yttrium used for radiosynoviorthesis

Background Chronic synovitis is one of the most frequent diseases rheumatologists and orthopedists are to deal with. In case of chronic synovitis the synovial membrane is proliferating some fluid. The proliferating membrane is creping into the cartilage causing pannus formation, then serious cartilage and bone destruction. Our aim is to stop this process. Radiosynoviorthesis (RSO) is used since 1952 as an alternative to arthroscopy and chemical synovectomy. The principle of the RSO is that high-energy, beta-emmiting isotopes are injected intraarticulary. The half-life shoud be short and the penetration according to the joint treated. The isotopes acts locally by destroing the cells of the hypertophic synovial membrane. The radioation burden of the isotopes used for RSO depends on the half-time, emitted energy, injected dose and the percent of leakage from the treated joint. The whole body radiation burden for Isotope usualy used for RSO: Y-90, Re-186, Er-168 are around 10 RAD. The radioation burden for Ho-166, avaible for the Inst. of Isotopes is 2 RAD. Objectives Comparison of the leakage of Y-90 and Ho-166 (two isotopses) used in Hungary for RSO. Methods 308 patients (170 Osteoarthritis (OA), 116 Rheumatoid arthritis (RA), 9 Psoriatic arthritis (PA), 4 JCA, 3 Villonodular Synovitis (VS), 3. Seronegatív spondarthritis (SNSA), 2 Arthriris urica, 1 SLE. treated with Y-90 or Ho-166 at the knee joint were compared by measuring the activity above the knee, inguinal lymph nodes and liver 2 days after the tratment. Results In case of Ho-166, above the liver 0.22% could be detected compared to the knee, and 0.32% above the inguinal lymp nodes. The avarage leakage was 0.54%. In case of Y-90 (2000nm) leakage above the lever 2,39% could be detected compared to the knee, In case of Y-90 (100nm) leakage above the liver 5,53% compared to the knee, and 11,61% above the inguinal lymp nodes. Comparing the two isotopes in cas of Y-90 the values were between 4-6%, in case of Ho-166 was less than 1%. Conclusions The use of Ho-166 for RSO is effective and safer than Y-90. The shorter half life of 26.9 hr. for Ho-166, the less amount of leakage results in a smaller radiation burden or the whole-body. Becouse of the physical characteristics Ho-166 can be used for large (knee) and medium size joints (hip, elbow, shoulder, wrist and elbow). The radiation burden can be compared to a spine radiological exam, in case of Y-90 this could be compared to a radiation burden of a CT exam.